When controlling an operation of an electrical device, an actual phase and an actual frequency of an electric quantity being associated with the operation of the electrical device may be important control parameters. For example, a rotor position and/or a rotor speed may be important parameters for controlling the operation of an electrical machine.
In particular, for a vector control of the electrical machine the rotor speed and the rotor position typically need to be determined. For example, the rotor position and the rotor speed may be determined by an encoder or by an estimator.
An encoder may be a hardware sensor which generates pulses when the electrical machine may be rotating. Based on a period between the pulses, the rotor position and the rotor speed can be calculated. Particularly, encoders are often widely used in electrical generators of wind turbines.
An estimator may estimate the rotor position and the rotor speed based on a model of the electrical machine by using measured electrical quantities of the electrical machine. For example, an estimator may be implemented in an inverter software of the electrical machine. An advantage of the estimator may be that it may merely be realized as software. Furthermore, the estimator may have lower maintenance costs and may be more reliable than the encoder.
However, the measured electrical quantities of the electrical machine may comprise higher harmonic components due to production tolerances and/or a design of the electrical machine. The estimator may be designed based on the assumption that the measured electrical quantities have ideal waveforms, for example sinusoidal waveforms. The higher harmonic components of the measured electrical quantities of the electrical machine may affect the accuracy of the rotor position and rotor speed estimation. In particular, an error of in the determined rotor position and rotor speed can significantly affect an efficiency of the electrical machine, for example a generator or a converter.
There may be a need to provide a better determination of a phase and of a frequency of an electric quantity being associated with an operation of an electrical device.